1. Field of the Invention:
This invention relates to an electronic clinical thermometer and, more particularly, to an electronic clinical thermometer of the predicting type.
2. Description of the Prior Art:
According to the prior art, a predicting-type electronic clinical thermometer predicts equilibrium temperature using a prescribed predictive mathematical equation and a condition which should be satisfied in order for a prediction to be valid. If we let t represent time and T a detected temperature, then a predicted equilibrium temperature Y at time t will be given by the following equation: EQU Y(t)=T(t)+U(t) (1)
where U represents a bias for prediction.
As described in EP-A No. 290,352 filed May 6, 1988, it can be assumed that the bias value is proportional to time as the first approximation with respect to a certain rate of change in temperature. If the relationship between the bias and time are obtainable with respect to various rates of change in temperature, it can be expressed as follows: EQU U(t)=An.multidot.t+Bn (2)
N=1, N where N is the number of dT/dt obtained)
Since the slope (An) and the intercept (Bn) in Eq. (2) can be represented by a linear relationship with respect to the rates of change in temperature, based on a number of experiments of measuring body temperature, An and Bn are given as: EQU An=a(dT/dt)+c (3) EQU Bn=b(dT/dt)+d (4)
Using Eqs.(2),(3) and (4), the following equation is obtained: EQU U(t)=(at+b)dT/dt+ct+d (5)
where
a=0.04321
b=0.38085
d=0.17734.
The condition which should hold for a valid prediction is as follows: EQU dT/dt=0.30/20 (.degree. C/sec) (6)
More specifically, when the rate of change in detected temperature with respect to time attains a predetermined value, namely when the aforementioned condition is realized during temperature detection, a buzzer incorporated within the electronic clinical thermometer is sounded to inform the person taking the temperature measurement of the fact that temperature detection has ended.
Though an accurate prediction can be made under fixed conditions in the example of the prior art described above, a change in the circumstances in which the thermometer is being used during temperature detection is not taken into account. Consequently, an accurate predicted temperature cannot be obtained if the circumstances of use change.
The foregoing will be described in greater detail. A curve shown in FIG. 9(a) indicating a change in a prediction variable (X) with time will be considered as an example. In accordance with FIG. 9(a), the prediction variable (X) gradually approaches an equilibrium value (Xe) with the passage of time. Therefore, the rate of change in the prediction variable with time (namely dX/dt) approaches "0" as the variable (X) approaches the equilibrium value (Xe). For example, dX/dt takes on a positive value and decreases monotonously from time t.sub.3 to time t.sub.4. However, when dX/dt is considered from time t.sub.1 to t.sub.2, as shown in FIG. 9(b), dX/dt takes on a positive value and increases monotonously from time t.sub.1 to time t', and X attains its maximum value at time t'. Further, dX/dt takes on a negative value and decreases monotonously from time t' to time t", and X attains its minimum value at time t". From time t" to time t.sub.2, dX/dt takes on a positive value and increases monotonously.
Assume that the foregoing variable (X) is applied to a predicted temperature (Tp). If the position of the tip of the probe at the end of the electronic clinical thermometer should happen to shift because of a change in the manner in which the thermometer is being held in the subject's armpit, for example, then the rate of change in the detected temperature with time (i.e., dT/dt) at this moment will suddenly decline and a state corresponding to the time region t.sub.1 -t.sub.2 shown in FIG. 9 will occur. In other words, the condition for a valid prediction expressed by Eq. (6) above happens to be satisfied and a value much lower than the equilibrium value which would have been attained originally is regarded as being the predicted temperature. Thus, there is a decline in the accuracy of prediction.